Polysilicon linewidth reduction using a BARC-poly etch process

Abstract

A process for forming a polysilicon line having linewidths below 0.35 mu m. The layer of polysilicon (20) is deposited over a semiconductor body (10). A layer of bottom anti-reflective coating (BARC) (30) is deposited over the polysilicon layer (20). A resist pattern (40) is formed over the BARC layer (30) using conventional lithography (e.g., I-line lithography). The resist pattern (40) has minimum dimensions of 0.30 mu m or greater. The BARC layer (30) is etched using the resist pattern (40) until the endpoint is detected. The BARC layer (30) and resist pattern (40) are then overetched using an isotropic etch having a selectivity of one-to-one between the BARC and resist. The overetch is a timed etch to control the linewidth reduction in the resist/BARC pattern. The minimum dimension of the pattern (50) is reduced to below 0.3 mu m. Finally, the polysilicon layer (20) is etched using the reduced width pattern (50).

What is claimed is: 
     
       1. A method of forming a polysilicon line, comprising the steps of: depositing a layer of polysilicon;   depositing a layer of bottom anti-reflective coating (BARC) over the polysilicon layer;   depositing a layer of resist over said BARC layer;   removing portions of said resist layer using a lithographic tool to create a resist pattern having a width greater than or equal to a minimum lithographic limit of the lithographic tool;   etching said BARC layer using said resist pattern until an endpoint is detected;   isotropically overetching said BARC layer and said resist pattern using a timed etch that has a selectivity between the BARC layer and the resist pattern of one to one to create a reduced width pattern;   etching said polysilicon layer using said reduced width pattern to create said polysilicon line.   
     
     
       2. The method of claim 1, wherein said BARC layer has a thickness greater than 1000 Å. 
     
     
       3. The method of claim 1, wherein said reduced width pattern has a width less than said minimum lithographic limit. 
     
     
       4. The method of claim 1, wherein said reduced width pattern has a width in the range of 0.1 to 0.29 μm. 
     
     
       5. The method of claim 1, wherein said reduced width pattern has a width less than the width of said resist pattern by an amount of 0.18 μm or less. 
     
     
       6. The method of claim 1, further comprising the step of depositing a top anti-reflective coating over said resist layer prior to said step of removing portions of said resist layer, wherein said step of removing portions of said resist layer also removes portions of said top anti-reflective coating. 
     
     
       7. The method of claim 1, wherein said steps of etching said BARC layer and isotropically overetching said BARC layer use an etch chemistry of CF 4 , O 2  and CHF 3 . 
     
     
       8. The method of claim 1, wherein said step of etching said polysilicon layer comprises the steps of: performing a breakthrough etch using an etch chemistry of SF 6  and HBr;   performing an endpoint etch using an etch chemistry of Cl 2  and HBr; and   performing an overetch using an etch chemistry of HBr and He/O 2 .   
     
     
       9. The method of claim 1, wherein said BARC layer has a thickness on the order of 2200 Å and said resist layer has a thickness on the order of 8000 Å. 
     
     
       10. The method of claim 1, wherein said isotropic overetching step is an overetch in the range of 10% to 150%. 
     
     
       11. A method of forming a polysilicon line having a linewidth less than 0.30 μm, comprising the steps of: depositing a layer of polysilicon;   depositing a layer of bottom anti-reflective coating (BARC) over the polysilicon layer;   depositing a layer of resist over said BARC layer;   depositing a layer of top anti-reflective coating over said resist layer;   removing portions of said resist layer and said top anti-reflective coating to create a resist pattern having a width greater than or equal to 0.30 μm using an I-line lithographic tool;   isotropically etching said BARC layer using said resist pattern until an endpoint is detected and then continuing the etch for a selected time to overetch said BARC layer and said resist pattern, wherein said etch has a selectivity between the BARC layer and the resist pattern of one to one such that a reduced width pattern having a width less than 0.30 μm is created;   etching said polysilicon layer using said reduced width pattern to create said polysilicon line.   
     
     
       12. The method of claim 11, wherein said BARC layer has a thickness greater than 1000 Å. 
     
     
       13. The method of claim 11, wherein said reduced width pattern has a width in the range of 0.1 to 0.29 μm. 
     
     
       14. The method of claim 11, wherein said reduced width pattern has a width less than the width of said resist pattern by an amount of 0.18 μm or less. 
     
     
       15. The method of claim 11, wherein said step of isotropically etching said BARC layer uses an etch chemistry of CF 4 , O 2  and CHF 3 . 
     
     
       16. The method of claim 11, wherein said step of etching said polysilicon layer comprises the steps of: performing a breakthrough etch using an etch chemistry of SF 6  and HBr;   performing an endpoint etch using an etch chemistry of Cl 2  and HBr; and   performing an overetch using an etch chemistry of HBr and He/O 2 .   
     
     
       17. The method of claim 11, wherein said BARC layer has a thickness on the order of 2200 Å and said resist layer has a thickness on the order of 8000 Å. 
     
     
       18. The method of claim 11, wherein said isotropically etching step continues after said endpoint for an overetch in the range of 10% to 150%.